This application relates to wireless communications in wireless communication systems including systems based on orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA).
Wireless communication systems use a network of base stations to communicate with wireless devices registered for services in the systems. Each base station emits radio signal that carry data such as voice data and other data content to wireless devices. Such a signal from a base station can include overhead load for various communication management functions, including information to allow a wireless device to identify a cell sector of a base station, to synchronize signaling in time and frequency. Each wireless device processes such information in the overhead load of each received signal prior to processing of the data.
OFDM and OFDMA based communication systems are based on the orthogonality of frequencies of multiple subcarriers and can be implemented to achieve a number of technical advantages for wideband wireless communications, such as resistance to multipath fading and interference. In an OFDM or OFDMA based wireless communication system, the wireless service to a geographic area is provided by dividing the area into a plurality of cells, which can be further divided into two or more cell sectors. The base stations, which conceptually locate at the center of respective cells of their coverage, transmit information to a mobile subscriber station (MSS) via downlink (DL) radio signals sent out from the base stations. A mobile subscriber station is also known as a mobile station (MS) or the wireless station. The mobile stations transmit information to their serving base stations via uplink (UL) radio signals.
The radio coverage of a network of fixed base stations may be limited due to various factors. Various structures may block the radio signals of certain base stations. For example, a tall building may shield a particular area from the radio signal from a base station, thus creating an undesired shadowing. At the edge of a radio cell, the signal strength can be weak and hence can increase the error rate in the wireless communications. One approach to mitigating these and other limitations is to increase the number of base stations in a given service area. In one implementation under this approach, one or more relay stations (RSs) can be deployed among certain fixed base stations to relay communication signals between a subscriber station and a base station, thus extending the coverage and improving the communication capacity and quality of the base station. A relay station may be a fixed transceiver or a mobile transceiver station depending on the specific conditions for deploying such as relay station. A subscriber station signals may hop through one or more RSs before reaching a serving base station. The proposed IEEE 802.16j standard provides Multi-hop Relay (MR) modes to use relay stations for enhanced coverage and service to subscribers. A multi-hop relay wireless network under IEEE 802.16j includes MR base stations (MR-BSs) to support Multi-hop Relay modes.